1. Field of the Invention
The present invention relates to an infrared sensor and, more particularly, to a thermopile infrared sensor.
2. Related Background Art
Conventional thermopile infrared sensors are shown in FIGS. 7 and 8. FIG. 7 shows the thermopile patterns of an infrared sensor. In this example, polysilicon 4 and aluminum 6, which are adjacent to each other, form a thermocouple. An infrared sensor shown in FIG. 8 is disclosed in Japanese Patent No. 2663612. In this example, a thermocouple made of a p-type semiconductor 106 and an n-type semiconductor 111 is formed on a cantilever 103. These infrared sensors measure the intensity of infrared rays incident on them on the basis of an electromotive force generated by the temperature difference between a hot junction and a cold junction of a thermocouple due to the Seebeck effect. Highly sensitive infrared sensors are implemented by a plurality of thermocouples in series.
In the infrared sensor shown in FIG. 7, however, since the polysilicon 4 and aluminum 6 are formed adjacent to each other, the thermocouple becomes large, and a plurality of thermocouples cannot be laid out at a high density. In the infrared sensor shown in FIG. 8, since the thermocouples are formed on the cantilever 103, the mechanical strength of the cantilever 103 decreases. In addition, since a infrared absorbing film 105 and the thermocouples are formed apart from each other, heat generated in the infrared absorbing film 105 is not efficiently transmitted to the thermocouples.
Japanese Patent No. 2663612 describes, as a prior art, an infrared sensor having a thermocouple made of an aluminum and a p-type diffusion layer resistor and points out that when aluminum is used, the sensitivity degrades because the Seebeck effect is small, and the thermal resistivity decreases. This patent also points out that the sensitivity degrades because the cantilever warps due to the bimetal effect.